Art of fractional distillation



Oct. 25 I9 27 N. E. LOOMIS ET AL ART OF FRACTIONAL DISTILLATION Filed July 21, 1922 a Sheets-Sheet 1 Nafhamel ELoorms and Warren K. Lew|5 N. E. LQOMIS ,ET AL ART 0F FRAGTIONAL DISTILLATION Filed July 21. 1922 s sheets sheet 2 Nathanll E LOOmIS and Warren K. Lewis.

Oct. 25, I927.

N. E. LOOMIS ET AL ART OF FRACTIONAL DISTILLATIONA Filed July 21, 1922 s sheets-sheets \uEW MQ m O W Patented Get. 25, 1927.

iiui'i' s'raras NATHANIEL E. LOOMIS, OF ELIZABETH, NEW JERSEY, AND WARREN K. LEWIS, OF NEWTON, MASSACHUSETTS, ASSIGNORS TO STANDARD DEVELOPMENT COMPANY.

A CORPORATION OF DELAWARE.

ART OF FRACTIONAL DISTILLATION.

Application filed July 21,

Our invention relates to fractional distillation and more particularly to the fractionation of hydrocarbon mixtures of the character of petroleum, having a large and indefinite number of constituents of increasing boilingpoints to produce simultaneously and continuously therefrom, a plurality of fractions each comprising more or less complex mixtures in and of themselves and each of said fractions containing substantially no constituents boiling above the upper limit of a predetermined range for said fraction.

In the practice of fractional disillation in the chemical industries generally, the conditions involved and the problems encountered are relatively clear cut and simple. In the case of alcohols and esters, etc., compounds and mixtures possessing a few very definite and-well separated boiling points only are concerned similarly in the case of coal-tar distillates, only a relatively few compounds, with definite and practicably spaced boiling lines of separation are dealt with.

On the other hand, in the petroleum industry the material in operation is a complex mixture of a legion of closely boiling compounds from very simple hydrocarbons on up to members of such complexity that their precise structure has not even yet been determined. Moreover, the lower and higher prima facie limits for such mixtures are extended by the fact that there are tenaciously held by solution further members Whose f normal physical state apart would be gase- I ous in the case of the lowest membersand solid in the case of the higher. Further complications arise from the fact that beyond the simplest-'members, for hydrocarbons'of a givennumber of carbon atoms, various isomers occur, and all these bring in complex overlappings in boiling points.

In the distillation of petroleum then, the boiling point temperature, starting at I its lower limit, mounts on a progressively sliding scale. If the distillate coming 0E ata given temperature were precisely only the hydrocarbon normally boiling at that temperature, close separations could be made,

ut with petroleum hydrocarbons such is far from thecase, for by reason of the peculiar 1922. Serial no. 576,611.

white cut will contain hydrocarbons which should be in the naphtha fraction and in the gas oil fraction, and the gas oil out will contain hydrocarbons which should be in the water'white fraction, etc. It is then necessary to re-distillthese cuts in the eifort to separate out and place the stray components,

and in the re-running it becomes necessary totake a heart-cut at the overlapping range between the naphthafand water white fractions, etc., for again further re-distilling, and in some casesthis must be further repeated. And even with the best overhead equipment heretofore used, a sharp separation is not realized.

By our invention we have now succeeded in attaining direct separations wholly or substantially free from overlap. The invention will be fully understood from the following description, reference being had also to the accompanying drawing, in which Fig. 1 is side elevation, partly in section,- of one form of apparatus contemplated in our invention;

Fig. 2 is a plan of the same;

Fig. 3 is a semi-diagrammatic view of a battery installationin accordance" with our invention, and

Fig. 4: is a similar view of an embodiment particularly useful as a re-run battery.

Referring more particularly to the drawings, the reference character A (see Fig. 1) designates a stillof any desired form, the formillustrated comprising a shell 1' traversed by tubular flues 2 through which hot products. of combustion from the-furnace pass on their way to stack 5-from the header flue-3 after having encountered the outside x5 transverse partitions or surfaceof the shell in the furnace chamber 4'; By thus applying heat within the'body of the oil, as well ase-xternally, a betterheat distribution is attained with crre-' V5 spondly lessened localized overheating le this particular construction of still is highly efficient and advantageous, it will be understood that in thebroader aspects of w the combination contemplated by us, modifim cations as to the type of heating of the still are included.

I From the still a vapor line 6 leads to a' fractionating, rectifying, or dephlegmating tower 7 havingv in its internal construction plates" with openings, with or without vapor-distributing caps and with overflow tubes,-t-he condition being that at each partition the vapors arebubbled through a layer of the liquid therei on. .A' simple form of such" partition is "made of die-stamped slitted sheet metal or advantageouslyof woven-wire fabric of desired mesh',jthe material beingiron, :alumi num, Monel metal, nickel or otheitmetal as 2 5 preferred.

Vapor connections 8 lead from th tower to a condenser-9, preferably'apartial condenser, constructed for example with tube sheets near each end and tubes extending therebetween for the passage of vapors and pipecon'nections 16 and 18- to the liquid space about the tubes, for a purpose to be referred to later more in detail. i From the partial condenser a-vapor-pipe 10 leads to a water cooled light worm condenser coil 11 from which pass connections to a receiver.

From the partial condenser a. refluxpipe 13 leads to the top of. the tower 7 for ,carrying condensate back thereto and from the bottom of thetower a runback pipe 14 leads to the still.

In the use .of'the apparatus as described crude oil or a distillate requiring re-runningforv closer fractionation is heatedin the still. Vapors rising therefrom. proceed to the tower and pass up through'the openings and bubble through the layers of liquid which soon collecton-theplates. In bubbling up through the layers of liquid, heavier constituents of thevapors' condense and join the liquid and at the same time any lighter constituents in the liquid "are vaporized and passonup. a I By these successive exchanges, on plate after plate, the vapors are averaged closer and closer on boiling point range and the reflux also is successively reduced. Vapors leaving the tower proceed on through the tubes of the partial condenser where a portion of the-constituents are condensed out a. andthe vapors then pass to the light condensiiig worm. The partial condenser furnishes an. adequate washing reflux'to the 'tower,lthe condensate flowing down through the'pipe 13 to'the top of the tower, In so suitable water-cooled With the equipment described, distillafar as affects the function of the tower, a total condenser may be employed at this point, so much of the condensate as is required being refluxed to the tower and the balance being run to a receiving tank. In working with. components of such close boiling point, we have found it to be of importance in order to produce desired fractions Whose boiling points lie substantially completely Within a predetermined range to provide 1 reflux in quantity greater than would be furnished by the operation of the tower itself, and in dealing with usual stocks it is advantageous to calculate for one to two. parts of reflux for each part of distillate; that is, the heat abstraction is suflieient to condense from one-half to two-- thirds of the total vapors passing from the top of the tower. Proper regulation of the temperature of the refluxing condenser may be secured by a suitable cooling medium, as water, but having regard for the co-operative functioning of the whole system we prefer to use the feed oil, this entering through pipe 15 and 16 (by-pass 17 being shut) and circulating about the vapor tubes. By usingtheby-pass 17 for by-passing cold feed oil in excess of that required to hold the -condenser at the desired temperature, a convenient and close regulation, of the quantity of reflux may be attained. The oil flowlng away by pipe 18 is sufliciently raised in temperature to be admitted to the still.

A fraction heavier than the end product obtained in condenser coil 11 may also be collected if desired by the pipe 12 from the tower above the feed plate and leading to a coil.

tion can be carried on by batch or continu ous operation as desired. In batch opera tion, successively higher boiling cuts may be obtained, each of self-contained range. In; continuous operation, the feed being-supplied at the same rate that distillate and bottoms are removed, the product will, be

of uniform character, andwill boil over a predetermined range dependent upon the outlet temperature of-the top of the tower, and the utility here lies in the completeness with which the light fragtious are stripped from the bottoms and vice versa. In contlnuous running the feed may be admitted to the still or preferably it may be admitted part way down the tower by a connection 19 in which case it is largelystripped of light fractions before reaching the still. This procedure insures a high initial boiling polnt of the bottoms.

From these illustrations it can be seen that he running conditions may be varied as requn ed to be closely adapted to the stock to be handled and the products to be made.

An advantageous embodiment of our invention in a continuous crude battery 'in stallation is shown in Fig. 3. In this, there is arranged a heating coil 37 mounted in a suitable furnace and heated thereby, a series of stills 21 to 25, or as many as desired to make up a given battery, being connected by a How line i8, and each still provided with appropriate overhead equipment. 'In the example shown, this comprises, for still 21, a vapor line :26 leading to. a fractionating tower 31, a line 38 from thence to a partial condenser 39, and a final condenser therebeyond, not shown, for simplification; for still 22, a vapor line 27, tower 32, partial condenser 4:1 and similarly a final condenser therebeyond, not shown; for still 23, a vapor line :28 leading to a partial condenser 33 and a final condenser, not shown; and similarly, for stills 24: and 25, vapor lines 29 and 30 respectively leading to partial condensers 3t and 35, and final condensers, not shown. The

stills 2l-25 are heated by any suitable means and at progressively higher temperatures from still to still in accordance with the distillates to be taken off.

The operation for this is as follows: The crude oil is supplied by pipe i7, passes into partial condenser 39, circulating about the vapor tubes thereof, and out by pipe to partial condenser 41, thence by pipe 42 to partial condensers 33, 34 and 35 in succession, thence by pipe 36 to the heating coil 37 where it is raised to the requisite temperature, depending upon the stock, and is then introduced into the fractionating tower 31, for example about midway. Lighter fractions vaporized pass on up the tower, and

the lightest constituents thereof proceed tothe partial condenser (being cooledtherein to the proper point by the heat interchange with the feed oil which is regulated'in amount by the by-pa'ss) and then go to the final condenser. The unvaporized portion and refiux flow down from plate to plate and along the pipe 26 to the still. Liquid condensed in the partial condensers 39 and 41 returns to the towers through pipes 43 and H.

Vapors rising from still 21 are also fract-ionated and sorted in the tower- The residual oil from still 21 flowing by a suitable fiXed-level outlet is picked up by a.

' pump 49 and forced into the tower 32 where it is stripped of its lightest content and passes down to the still 22 where it is further heated and vapors are given off to. the tower for fractionation. The residual oil from still 22 passes to still 23' where it is further heated and vapors are given off to the condenser system. The residual oil from still 23 passes on in succession to the remaining stills in the battery, being progressively heated and relieved of vaporizable constituents for the respective temperatures maintained.

We have illustrated the fractionating towers as applied to the stills of the light end of the battery, as in general it is here that a sharp separation is desirable and especially useful;' we contemplate, however,

combining the fractionating tower arrangement in with any or all stills where it is desired to specialize on a sharp primary separation. I

Our invention is very advantageous in rerunning the overlap'in cuts previously taken by overhead equipment of the usual type, as for example the overlap hetweennaphtha and water white distillate. As an example of an installation convenient in such connection, attention is directed to Fig. 4:, in which is indicated a still 51 suitably heated and with vapor line 53 to a tower 54, a vapor pipe 55 therefrom to partial condenser 56 and tinal off-take 57 in turn to condenser 58. A reflux pipe 59 connects from the partial condenser 56 back to the top of the tower 5-.t and from the bottom thereof a run back pipe (SO leads to the still. A second still 52, suitably heated at a higher temperature than still 51, has an analogous vapor-line 61, tower 62, vapor-pipe 63, partial condenser 64:, final off-take 65 and condenser 66; also a a reflux pipe 67 from the partial condenser, and a run back pipe 68 from the tower. Additional stills may be combined in this battery if desired, but we regard a two-still unit as generally desirable for straight rerun 'duty.

\Yith this installation the feed is supplied from line 69 by pump 70 through the line 71 the tubes therein, pas'ses thence by pipe 72 to the partial condenser 64 and thence by pipe 73 to thetow er 54 and thence by the reflux'run back 60 to the still. This still with its overhead equipmentremoves the naphtha, and the bottoms are then passed by pump 75 and line 76 to the second towe-r- 6:2 and proceed therefrom by the run back pipe 68 to the second still 52. This still with its overhead equipment removes the water white. The bottoms from the second still pass through a pipe .77 to a cooling coil 78 and pump 79 to the gas oil tank.

As an example, on a refinery re=run stock, the first still removed all of the naphtha, an overhead of 40%, and the bottoms on being. passed to the tower andsecond still gave up all the water white,'an additional 45%; the bottoms therefrom was a gas oil wholly devoid of lighter fractions.

Having, in the foregoing, referred to hydrocarbons of the character of petroleum, it is to be observed that such expression designates not only petroleum proper and its derivatives, but also other oils containing hydrocarbons of this character, such as shale oils, lignite oils, brown-coal oils, and lowtemperature oils retorted from carbonaceous material.

iali) to the partial condenser 56, circulates about elty as broadly While-in describing our invention we have referred to certain specific examples of invention is to be regarded as limited only as defined in the following claims, in which y it is our intention to claim all inherent novas the prior art permits. WVhat we claim is: 1. The improvementin the art of distilling petroleum oils 'having'a large number of constituents of different boiling points to produce simultaneously and continuously (1) a light distillate containing substantially all the low-boiling constituents of the original oil and substantially no constituents boiling above a predetermined. temperature, and (2) a residual product containing substantially all constituents in the original oil of higher boiling point'than those in said light distillate and substantially free from constituents of said .light distillate, which process comprises continuously introducing the original oil into a fractionating zone at an intermediate point thereof, flowing the oil downwardly 'therethroug supplying heat adjacent the lower portion of said zone to produce a substantial amount of vapors, thereby permitting the formation of adequate reflux by condensation of such vapors, conducting the vapors upwardly through said fractionating zone in countercu-rrent to the descending oil, the proportion of said Vapors being suflicient to secure the stripping from said oil of substantially ,all the low-boiling constituents desired in the said light distillate, so that the oil entering the heating region is substantially free from.

constituents of said light distillate, cooling to hold a substantially constant temperature in the upper portion of the fractionating zone, while abstractingnotless than that amount of heat which would be taken up by refluxing to the fractionating zone about one-half of the vapors leaving the same, collecting and removing as the desired light distillate the product of condensation of the vapors leaving the upper portion of. the

ating tower,

feed oil to or from the point of a secondand'independentfractionoperating said second tower under substantially the same conditions as said first tower,

collecting and removing as a heavy distillate the product of condensation of the vapors leaving the top of the second tower, and continuously removing residual oil from the base of the second tower.

8.,Process of continuously distilling hydrocarbon oil of the character of petroleum to obtain products having a relatively narrow range of boiling points, said process comprising distillingthe oil, passing vapors therefrom through a fractionatin zone, preheating at least a portion '0 feed oil passing to the distilling zone by indirect .heat exchange with vapors from said fractionating zone, thereby partially condensing such vapors, introducing the preheated feed,

oil into an intermediate portion of said fractionating zone and pors, regulating the y by-passing to the fractionating zone any flowing it downwardly j therethrough in pontact with ascending -va portion. of the feed oil in excess ofthat re-' r quired in, said heat exchange, vapors passing from the partial condensation zone.

of hydrocarbon oils of the character of pcand condensing 4. Process for the fractional distillation V troleum, which comprises distilling the oil i in a plurality of series-connected zones,

fractionating vapors from each zone, preheating feed oil by passing it in indirect heat exchange not of such fractionation, whereby such va-v pors are partially condensed, diverting the partial condensing,

with vapors issuing as a final prod a zones to regulate the amount of condensation, passing the preheated feed oil into an interl mediate portion'of zone, and forwarding residual oil from each distilling zone to the fractionating operation of a succeeding distillation. A NATHANIEL E. LOOMISQ- WARREN LEWIS.

the first fractionatin'g v 80 amount of condensation i a 

